B. Chouet P. Dawson A. Arciniega-Ceballos 2003 <p><span>Following an initial phreatic eruption on 21 December 1994, activity at Popocatepetl has been dominated by fumarolic emissions interspersed with more energetic emissions of ashes and gases. A phase of repetitive dome-building and dome-destroying episodes began in March 1996 and is still ongoing at present. We describe the long-period (LP) seismicity accompanying eruptive activity at Popocatepetl from December 1994 through May 2000, using data from a three-component broadband seismometer located 5&nbsp;km from the summit crater. The broadband records display a variety of signals, with periods ranging in the band 0.04–90&nbsp;s. Long-period events and tremor with typical dominant periods in the range 0.3–2.0&nbsp;s are the most characteristic signals observed at Popocatepetl. These signals appear to reflect volumetric sources driven by pressure fluctuations associated with the unsteady transport of gases beneath the crater. Very-long-period (VLP) signals are also observed in association with LP events and tremor. The VLP signals which accompany LP events display Ricker-like wavelets with periods near 36&nbsp;s, whereas VLP signals associated with tremor waveforms typically show sustained oscillations at periods ranging up to 90&nbsp;s. The spectra and particle motion patterns remain similar from event to event for the majority of LP and tremor signals analyzed during the time span of this study, suggesting a repeated, non-destructive activation of a common source. Hypocenters determined by phase pick analyses of selected LP events recorded by the seven-station, permanent Popocatepetl short-period network suggest that the majority of these events are confined to a source region in the top 1.5&nbsp;km below the crater floor. The repetitive occurrences of VLP signals with closely matched waveform characteristics are consistent with a non-destructive reactivation of at least two sources. One source appears to coincide with the main source region of LP seismicity, whereas the second is a deeper source whose activity appears to be intimately linked with episodes of monochromatic tremor.</span></p> application/pdf 10.1007/s00445-002-0248-8 en Springer Long-period events and tremor at Popocatepetl volcano (1994–2000) and their broadband characteristics article